The concept of multiplexing packet data flows, including Real-Time Transport protocol (RTP) flows together into a single aggregate flow is a concept that is addressed in a number of Internet Engineering Task Force (IETF) Internet drafts. Multiplexing RTP flows is desirable, because it can reduce the bandwidth usage of Wide Area Network (WAN) links and decrease the RTP packet rate incident on edge routers. In addition, the multiplexing of RTP flows reduces the burden of administering networks, for example in connection with the configuration of quality of service levels. In addition, multiplexing RTP flows can increase the scalability of existing quality of service schemes.
RTP multiplexing is a session layer technique that packetizes the different streams to create a compound packet containing the individual payloads from different RTP sessions as well as some additional control information. One shortcoming of RTP multiplexing is that it does not provide a conferencing capability to sum the audio streams together. Another shortcoming of RTP multiplexing is that every channel has to be encoded and decoded by a codec.
As can be seen in FIG. 1, a signal processing system 100 according to embodiments of the prior art comprises a plurality of source signals 108a-M that are passed through their own codec 112a-M prior to being multiplexed at the RTP multiplexer 116. The RTP multiplexer 116 causes each individual encoded signal to be combined into an aggregate signal and packetized according to RTP standards. The packetized signal is then transmitted across a communication network 104 to the receiving end where the signal is de-multiplexed at an RTP de-multiplexer 120 and the data from the packet is separated into individual channels. Thereafter, each signal is passed through another codec 124a-M where it is decoded. The result is a plurality of individual signals that are treated separately from one another. A downside to this solution is that if conferencing of the signals is desired, then each separate signal has to be provided to a mixing stage 128 where the signals can be summed at a summing point 132. Only thereafter can a coherent conference signal of the multiplexed streams be provided to a recipient.
As can be appreciated, prior multiplexing solutions do not lend themselves to conferencing applications particularly well because of all the excess processing overhead involved. It would be desirable to multiplex a plurality of signals in such a fashion that they can be easily utilized in conferencing applications without excessive processing steps.